Oregon Public Broadcasting

A state investigation into why 24 high school football players ended up in hospital after a grueling training session, has found a series of factors to blame.

One problem was short, repetitive bursts of resistance training -- focused tightly on the upper body -- so soon after a summer vacation without rigorous workouts.

Add to that, high temperatures and players not drinking enough water, and you have a recipe for problems.

Players suffered severe pain in their triceps muscles; three required surgery. Five had creatine levels 100-times the upper limit. Creatine is a blood test marker for muscle injury.

State epidemiologist Katrina Hedberg says the tests are inconclusive for supplements because they don't distinguish between creatine from supplements, and naturally occurring levels.

Katrina Hedberg: "I must say there is nothing to indicate that this kind of protein supplementation was any different in this high school football team than any other team or that players elsewhere might have taken. So we have nothing to indicate that that in anyway contributed to this outbreak."

Health officials have issued a list of recommendations to help coaches prevent similar injuries.

The investigation will continue to quote: "better characterize this cluster of illness."